Ser. No. 79,183 filed July 29, 1987 in the name of Abboud Mamish and assigned to The Kendall Company, assignee of the present invention discloses conformable flame-retardant pressure-sensitive adhesive tapes that are particularly useful in wrapping irregular surfaces, e.g. wire harness wraps where conformability is essential to good adhesive contact.
In general, industrial adhesive tapes of the type known as duct tapes consist of a pliable film base, e.g. a polyolefin; a reinforcing fabric or scrim of cotton or a synthetic fiber, and an adhesive layer, e.g. a rubber-based adhesive coating.
Particularly efficacious tapes of this general description are described and claimed in U.S. Pat. No. 4,303,724 issued to Sergeant and Thomas and assigned to The Kendall Company, assignee of the present invention. In accordance with their patent, the tear characteristics of such tapes having low-count reinforcing fabrics is greatly improved if the fabric comprises texturized or "false-twist" yarns in the filling direction. For instance, in the Specific Embodiment of the invention in Col. 2, a gauze fabric was constructed using 20 yarns per inch of cotton in the warp (machine direction) and 12 false twist polyester yarns in the filling (cross) direction. When torn by hand, the tear properties of the tape imparted by the 20.times.12 fabric achieved an even tear previously attainable only by the use of appreciably higher count fabrics.
In the tape described in the specific embodiment, the film backing was a low density polyethylene (LDPE) 4 mils thick and the adhesive, a rubber-based adhesive, was 6 mils thick. These recited thicknesses for the film backing and adhesive coating are fairly illustrative of the thicknesses generally utilized for duct tapes.
While tapes of such thicknesses are of course quite satisfactory in terms of flexibility for their intended usage, e.g. as duct tapes, they lack the flexibility and conformability for wrapping smaller objects, particularly smaller objects of irregular shape.
Broadly speaking, the invention described in the aforementioned application is directed to industrial adhesive tapes which have a reinforcing fabric scrim for increased strength and dimensional stability but yet possess the conformability for use as a protective wrap for irregularly shaped articles. The scrim also facilities even tearing in the cross direction. More specifically, it relates to an adhesive tape of this description which possesses the physical properties required for use as a harness wrap, for wire splices and other such industrial applications. For such industrial applications, the tape should be low cost, liquid impermeable, chemical resistant, flame retardant, non-corrosive and evenly tearable in the cross direction (CD) as well as being conformable so as to adhere to the irregular contours of the article to be wrapped. This combination of requirements for the intended industrial applications in turn present several obstacles which must be overcome in order to provide the desired tape.
With respect to the reinforcing fabric, synthetic fibers such as polyesters as a class have the requisite qualities and are also of acceptable low cost. However, suffer the disadvantage of possessing poor anchorage to polymeric backings or other polymeric substrates. Consequently, when the thickness of the backing layer (e.g. polyethylene) is reduced in any effort to achieve the desired conformability which may be obtained by employing thinner films, the anchorage of the scrim to the backing drops. The resulting product accordingly lacks the structurable stability for marketability. Cotton fibers on the other hand, may provide acceptable anchorage to such a thinner backing. However, they are quite flammable and consequently must be treated with a flame retardant and, moreover, are more expensive. For these reasons, cotton scrims cannot be employed in accordance with this invention and it is therefore necessary to employ synthetic fiber scrims in the preparation of the thin, conformable tapes envisioned by the present invention. This in turn requires some way to provide the acceptable anchorage which is not inherent in the use of synthetic fiber scrims with thin backings.
The task of the invention in the aforementioned Ser. No. 79,183, simply stated, may be said to be to solve these problems so as to provide an adhesive tape having the described properties and which maybe used, for example, by the automotive industry for harness wraps.
As is disclosed in the copending application, Ser. No. 79,183, the task is solved by providing an adhesive tape comprising: (1) a water-impermeable backing layer, e.g. low-density polyethylene (LDPE), on the order of 1-3 mils thick containing a flame-retardant; (2) an evenly tearable synthetic fiber scrim; (3) a flame retardant adhesive layer, preferably a rubber-based adhesive; and (4) a tie coat layer between the backing and the scrim which, when applied, at least partially fills the interstices between fibers of the scrim so as to provide surface contact with the underlying adhesive layer, the tie coat providing a strong bond at both the tie coat-backing interface and the tie coat-adhesive and scrim interfaces, thereby providing a laminar product possessing the desired anchorage and structural stability.
In the preferred embodiment of the invention, the tape is provided by coextruding the backing material and tie coat onto the scrim and thereafter applying the adhesive coating.
The task of the present invention may be said to be two-fold, namely: (1) to provide still greater conformability for the contemplated usage; and (2) to eliminate or at least materially reduce the amount of flame retardant which need be put in the backing layer for uses where optimum flame retardancy is an essential property of the adhesive tape.